The CMS detector comprises 100 million individual detecting elements, each looking for
tell-tale signs of new particles and phenomena—40 million times a second. It is one of the most
complex and precise scientific instruments ever constructed. It will operate 100 m underground
at the French village of Cessy, just across the border from Geneva in Switzerland, for at least ten
years starting in late 2007.
CMS Parameters
12 500 t
21 m long
15 m diameter
The huge size of CMS belies the complexity within.
A technician assembles
one of the components
of the inner tracker using
5-micron thick wires.
The large pieces of CMS,
weighing between 200
and 2000 tonnes each, are
lowered 100 m into the
cavern and then assembled into position.
A Worldwide Enterprise Solving some of the mysteries of the Universe is only possible
with the involvement of scientists, engineers and students from a multitude of disciplines. Pieces
of CMS have been designed and constructed in institutes around the world, as well as in industry,
before being brought to CERN for the final assembly. The data analysis will then be another worldwide endeavour, made possible through innovations in computing technology such as the Grid.
A researcher and a PhD
student work together
to cable and test some of
the readout electronics of
CMS.
Some collaborators gather in the assembly hall to
celebrate the end of construction of an element of
CMS.
CERN
European Organization
for Nuclear Research
CH-1211 Geneva, Switzerland
CMS
Compact Muon Solenoid
Colliding
protons at unprecedented energies
To create
conditions that existed a fraction of a billionth of a
second after the Big Bang
To look for
new particles such as the Higgs boson, supersymmetric
particles, mini black holes, gravitons…
To answer
Where does mass come from?
What constitutes dark matter?
How many dimensions of space are there?
Can we make further progress towards a unified theory
that can explain ALL physical phenomena?
CMS Collaborators
38 countries, 182 institutes
1050 physicists, 450 students
1000 engineers & technicians
Only results from experiments can
reveal Nature’s deeper workings.
CMS is such an experiment
Communication Group, August 2006
CERN-Brochure-2006-007-Eng
To find out more about all aspects of CMS, visit our web site at: http://cms.cern.ch
www.cern.ch
http://cms.cern.ch
The Detector and Detectives
CMS is a large technologically advanced detector
comprising many layers, each of which is
designed to perform a specific task. Together
these layers allow CMS to identify and
precisely measure the energies/momenta
of all particles produced in collisions at
CERN’s Large Hadron Collider (LHC).
Tracker
Pattern Recognition
Finely segmented silicon sensors
(strips and pixels) enable charged
particles to be tracked and their momenta measured. They also reveal
secondary vertices (from the decays
of unstable particles).
New particles are typically unstable and rapidly transform into a cascade of lighter, more stable and better understood particles. Each
type of particle travelling through CMS leaves behind a characteristic pattern, or ‘signature’, in the different layers, allowing them to
be identified. The presence (or not) of any new particles can then be
inferred.
��
��
�������
�������
���������������
�����������
Electromagnetic Calorimeter
������
�����������
Around 80 000 crystals of lead tungstate (PbWO4) are used to measure
the energy of incident electrons and
photons.
���
���
���������������
��������
���
���
�����������������������������
������������������
���
���
���
���
����
��������
����
��������������������������
�����������������������������
������
Trigger System
To have a good chance of producing a rare particle, such as a Higgs
boson, the particle bunches in the LHC collide up to 40 million times
a second. Particle signatures are analyzed by fast electronics to save
only those events (~100 per second) most likely to show new physics—reducing the data rate to a manageable level. These events are
stored for subsequent detailed analysis.
Hadron Calorimeter
Layers of dense material (brass or
steel) interleaved with scintillators
(plastic or quartz) allow the estimation of the energy of hadrons, that is,
particles such as protons, neutrons
and pions.
Muon
Muon
Muon Detectors
Superconducting Solenoid
Passing 20 000 A along a 13 m long,
6 m diameter coil of niobium-titanium superconductor, cooled to
–270°C, produces a magnetic field
of 4 teslas. This field bends the trajectories of charged particles, allowing their separation and momentum
measurement.
��������������
Muon
Three varieties of detector are employed by CMS to identify muons
(essentially heavy electrons) and
measure their momenta: drift tubes,
cathode strip chambers and resistive
plate chambers
�����
�����
Data Analysis
�����������������������
���������������������
Physicists from around the world
use cutting-edge computing techniques (such as the GRID) to sift
through millions of events from
CMS to produce plots such as the
one on the left (a simulation) that
could indicate the presence of
new particles or phenomena.
�����
�����
������������
�����
����
����
����
����
����
���
���
���
���
���
���
Muon
���
���������